Tropical Storm Isaac, Part 2: Isaac Moving Into The Gulf Of Mexico-Hurricane Warnings For Morgan City, LA/MS/AL & FL Panhandle To Destin, FL

[WishingForWarmWeather]

How big/what kind of an impact will the center relocation have on the track?

[phil882]

How big/what kind of an impact will the center relocation have on the track?

It will probably result in an earlier landfall time... and perhaps a further west track given that it will track further west before the weakness has a chance to develop to its northeast. If it can come under the influence of the amplifying mid-level ridge before the weakness develops, it will probably be too far to the east to recurve the tropical cyclone. Thus, it tends to support the further west trends in the modeling.

[jconsor]

The ECMWF's rapid intensification just before landfall is hard to believe given the rapid decrease in TCHP just off the MS/LA coast, but it does have a nearly ideal upper pattern in the 18 hours before landfall.

200 mb - 24 hours. Note the band of stronger southerly winds associated with the ULL to the west of Isaac impinging on its circulation.

200 mb - 48 hours. Note the anticyclone nearly over Isaac and the circular ring of <10 kt winds at 200 mb surrounding Isaac.

[HurricaneJosh]

I am once again reminded that intensity forecasting is a complete crap shoot. The science just isn't there. Maybe in twenty years.

[andyhb]

It was in the 940 hPa range on the 12z run. The two primarily reasons for the weaker intensity are further west postion initially, and the upper level low over the W GOM taking slightly longer to get out of the way, so it imparts south to southeasterly shear on Isaac for another 12-18 hours or so.

Minimum I saw was 949...

[Superstorm93]

Eye showing up on radar

[Ed Lizard]

I am once again reminded that intensity forecasting is a complete crap shoot. The science just isn't there. Maybe in twenty years.

Same general target for GFDL and HWRF, St Mary Parish (parish seat, your old stomping grounds of Franklin). GFDL is a strong TS, HWRF is a major hurricane. SHIPS splits the difference. Landfall intensity is a mytery indeed. GFS has been semi-consistent.

I think NHC forecast is a good compromise.

[dan88]

The rainfall rates reported on this recon mission which is just starting up appear to be incorrect, every observation (~40 thus far) since hitting mission altitude has reported 12-15mm/hr

[PatrickSumner]

NHC now only going with a category 1 landfall. (90MPH) In my opinion, things are looking up for the Northern Gulf Coast.

[dan88]

000

URNT12 KNHC 270859

VORTEX DATA MESSAGE AL092012

A. 27/08:44:30Z

B. 25 deg 22 min N

084 deg 14 min W

C. 850 mb 1344 m

D. 44 kt

E. 291 deg 37 nm

F. 042 deg 45 kt

G. 306 deg 82 nm

H. 989 mb

I. 16 C / 1529 m

J. 23 C / 1520 m

K. 17 C / NA

L. NA

M. NA

N. 1345 / 8

O. 0.02 / 2 nm

P. AF303 2509A ISAAC OB 05

MAX FL WIND 45 KT NW QUAD 08:18:30Z

[thewxmann]

NHC now only going with a category 1 landfall. (90MPH) In my opinion, things are looking up for the Northern Gulf Coast.

Yeah, and everyone was throwing Katrina scenarios out just 12 hours earlier.

Goes to show how tricky TC forecasting is.

[CoastalWx]

That's a healthy VDM temp sample there. I wouldn't sing to the mountains just because the NHC has 85mph winds. Intensity is tricky with these storms.

[Stebo]

That's a healthy VDM temp sample there. I wouldn't sing to the mountains just because the NHC has 85mph winds. Intensity is tricky with these storms.

Agree, a good 12-24 hour period of intensification and this could easily be 90mph or higher.

[dan88]

Shear seems to have diminished a bit, as at the very least Isaac has been maintaining a good amount of precip South of the center for some time now.

[dan11295]

Both BYX and TBW long range radars are now showing convection wrapping entirely around the core and deep convection right at the center. Also noticing the IR loop indicating some better outflow to the south, implying relaxation of the southerly shear

[CoastalWx]

That ULL still hanging around and a reminder that they never clear as quickly as forecasted.

[Solak]

From the G-IV research plane

@HRD_AOML_NOAA

#NOAA42 just passed through the center of #Isaac. South side has some small rainbands wrapping around center, but know eyewall forming. (39 min ago)

#NOAA42 radar is showing few rainbands beyond 50 nm southeast of #Isaac center. All the action is still north of center. (14 min ago)

#NOAA42 radar is painting southwest FL near Naples and Ft. Meyers as we track to a point 105 nm east of #Isaac center. Hint of eye forming. (2 ago)

[HKY_WX]

I think it's obvious now the ULL is not out of the way yet and is inhibiting development, but looking at how quickly the ecmwf strengthens this off the coast of LA/MS(roughly 20mb drop between hr 42 and hr 60 to sub 952mb), I caution anyone to breath a sigh of relief. That's just crazy talk at this juncture. Canes coming into LA/MS at this angle historically strengthen and have favorable conditions right up till landfall. Given the slow movement and track (pretty much a worse case scenario track for NO), I would be extrememly nervous if I lived anywhere near there. This could be a complete disaster for them if we have a sub 950mb cane heading NW towards NO at 3mph.

[toxictwister00]

From the G-IV research plane

@HRD_AOML_NOAA

#NOAA42 just passed through the center of #Isaac. South side has some small rainbands wrapping around center, but know eyewall forming. (39 min ago)

#NOAA42 radar is showing few rainbands beyond 50 nm southeast of #Isaac center. All the action is still north of center. (14 min ago)

#NOAA42 radar is painting southwest FL near Naples and Ft. Meyers as we track to a point 105 nm east of #Isaac center. Hint of eye forming. (2 ago)

HRD/AOML/NOAA ‏@HRD_AOML_NOAA

#NOAA42 is heading into forming eye of #Isaac. Radar shows rainband has rotated to N of center and merging with major band NW of center.

[OSUmetstud]

Well, shear doesn't seem like it should be much of a problem anymore. Goes shear analysis has about 5 kt over the center and the 06z SHIPS run has 3 kt of shear for 12z. Outflow is expanding, especially to the west as the center moves closer to the center of the upper level anticyclone. Let's see what it can do today.

[dan11295]

At any rate if the ULL doesnt move out of the way for 24+ hours we shouldnt expect anything more than slow intensification until then.

[Solak]

@HRD_AOML_NOAA

#NOAA42 radar suggests an eye is forming in #Isaac.It is elliptical with major axis WNW-ESE and diameter 30 nm. In major bands to west.

[Ed Lizard]

6Z GFS isn't a major at landfall anymore. Close, but no cigar. Not sure what exact reduction from 900 mb to surface would be when pressure is 970mb, but I'd think it is still showing a solid Cat 2. Ignoring the resolution of a global, and maybe it showing a Cat 2 is actually showing a Cat 3. But GFS has been pretty intense, so I'm not sure how bi a factor resolution plays.

Track wise, it'll have to turn sharply soon to landfall in Florida..

[Ed Lizard]

Latest satellite looks kinda interesting. Either an eye trying to form, or just a break in convection/dry air. Will have to see if it is persistent. ( I am currently guessing it is the latter.)

if you're reading the thread, the NOAA G-IV is sending out tweets that the NOAA WP-3D is seeing an eye forming on radar.

[wxsmwhrms]

A few observations this morning. I really thought after watching the way Key West radar was developing last night before bed that this thing would be a bit better organized by now. However, the fact that the NOAA aircraft states that an eye is forming, and the appearance of some stronger winds closer to the center than just the light winds that had been being observed in previous passes, suggests that maybe there is an inner core developing now. Also, a bit more push of outflow to the south and the appearance of the some convection south of the center would appear to imply that some abating of the southerly shear is occurring.

Today is the day that if we are going to see this thing make a run it should start to happen. GFS/EC shows substantial deepening starting later today and continuing right up to landfall. 12Z EC yesterday showed 988 mb at 12Z today which is going to be pretty darn close. I like the current NHC forecast of a high end cat 1 at landfall - if it can take a track which enables it to stay over water a bit longer or gets better organized quicker obviously a category 2 is still well within reach.

[CoastalWx]

It still may be dealing with relatively drier air to the east as evident on WV and meso analysis of PWAT and KI.

[gkrangers]

A few observations this morning. I really thought after watching the way Key West radar was developing last night before bed that this thing would be a bit better organized by now. However, the fact that the NOAA aircraft states that an eye is forming, and the appearance of some stronger winds closer to the center than just the light winds that had been being observed in previous passes, suggests that maybe there is an inner core developing now. Also, a bit more push of outflow to the south and the appearance of the some convection south of the center would appear to imply that some abating of the southerly shear is occurring.

Today is the day that if we are going to see this thing make a run it should start to happen. GFS/EC shows substantial deepening starting later today and continuing right up to landfall. 12Z EC yesterday showed 988 mb at 12Z today which is going to be pretty darn close. I like the current NHC forecast of a high end cat 1 at landfall - if it can take a track which enables it to stay over water a bit longer or gets better organized quicker obviously a category 2 is still well within reach.

989 with 11 knots on a center sonde. Looks like you have your 988.

[wxsmwhrms]

It still may be dealing with relatively drier air to the east as evident on WV and meso analysis of PWAT and KI.

I think that's more likely an issue than any "warm mid level air" that somebody asked about. BTW, the NOAA aircraft send a tweet that says that the circulation is now well aligned from 0 to 6 km with just a slight northward tilt.

BTW, is it just me, or does it seem to be going a bit right of the forecast based on the last few VDM messages?

[winterymix]

BTW, is it just me, or does it seem to be going a bit right of the forecast based on the last few VDM messages?

Maybe 4 miles to the right.

[Solak]

SUMMARY OF 800 AM EDT...1200 UTC...INFORMATION

----------------------------------------------

LOCATION...25.7N 84.7W

ABOUT 185 MI...295 KM WSW OF FT. MYERS FLORIDA

ABOUT 360 MI...575 KM SE OF THE MOUTH OF THE MISSISSIPPI RIVER

MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H

PRESENT MOVEMENT...WNW OR 300 DEGREES AT 14 MPH...22 KM/H

MINIMUM CENTRAL PRESSURE...988 MB...29.18 INCHES